"I do not find my key."
Translation:Yo no encuentro mi llave.
i know i'm too late for you but "no puedo encontrar mi llave" is more like "i can't find my key". "i don't find my key" is a lot less common than "i can't find my key" in english but i think that duo's logic (in this case) is to translate as close as possible, for better or worse.
Encuentro means "I find" whether you are a guy or a girl before nouns you need to use "mi" "mio" comes after
It's not great English. You would always say "I can't find my key", not "I don't find it".